To satisfy the increasing demands for wireless data traffic since commercialization of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) communication system or a pre-5G communication system. For this reason, the 5G or pre-5G communication system is referred to as a beyond-4G or post long term evolution (LTE) system.
To achieve high data rates, deployment of the 5G communication system in a millimeter wave (mmWave) band (for example, a 60-GHz band) is under consideration. For the 5G communication system, beamforming, massive multiple input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna techniques have been discussed in order to mitigate the path loss and propagation distance of waves in the mmWave band.
Further, for network improvement in the system, technologies such as evolved small cell, advanced small cell, cloud radio access network (RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation have been developed in the 5G system.
Besides, advanced coding modulation (ACM) techniques such as hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access techniques such as filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed in the 5G system.
In a multi-user MIMO (MU-MIMO) system, the same resources are allocated to a plurality of users, using downlink (DL) channel information, and beamforming is applied to the users to avoid interference between the users, thereby increasing a sum rate. If the channel information is accurate, beamforming prevents a signal of one user from interfering with a signal of another user, and thus even though a receiver is designed in the same manner as in a single input single output (SISO) system, reception performance may be increased. However, a channel estimation error and quantization-incurred information loss during transmission of DL channel information on an uplink (UL) make it very difficult to transmit accurate channel information to a transmitter. In this situation, beams formed based on inaccurate channel information leads to imperfect interference control, thereby degrading reception performance.
Reference signals (RSs) are transmitted in an orthogonal pattern in the MU-MIMO system. That is, an RS for one user and an RS for another user are the same signal transmitted with different codes in an orthogonal pattern. Ideally, a user may receive a signal without the influence of a signal of another user, using such an orthogonal pattern, and perform channel estimation. In most cases, however, a user has difficulty in fully reflecting a channel change which is attributed to a frequency change or occurs with passage of time during channel estimation, and thus in estimating accurate channel information. Further, since a received signal is processed on the assumption of perfect interference cancellation in the MU-MIMO system, inaccurate channel information causes the degradation of reception performance.
In the MU-MIMO system, the performance of a receiver depends on the accuracy of a beam formed by a transmitter. However, since the MU-MIMO system deals only with processing of a received signal on the assumption that interference from other users has been canceled by beamforming in the transmitter, it is vulnerable to interference from beams imperfectly formed due to quantization or a channel estimation error during transmission of channel information on a UL. Accordingly, a multi-user signal detection operation is needed to process the interference from the imperfect beams, but has a limited performance increase in view of imperfect channel estimation.
In this context, there is a need for a method for accurately estimating a DL channel in the MU-MIMO system.
The above data is presented as background data only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.